Dear Mems-talk friends,

I am currently working on depositing (300A)Ti/1000A(Al) metals on GaN. I am
using S1813 as my photoresist. i am spinning the photoresist at 3000rpm for
30s. My deposition rate on the e-beam is 7-10 A/s for both metals.The vacuum
pressure inside the chamber of the e-beam is 9e-7 before doing my deposition.
i use Acetone for the lift-off process. For some reason when i stick the
sample in acetone without ultrasonic agitation, the lift-off process does not
happen, basically the sample just sets there and nothing happens. On the other
hand, when i use the ultrasonic agitation, all the metals on my sample will
lift-off and the lift-off process fails!! it seems that the metals are not
sticking very well to the sample for some reason??

Keep in mind that i cleaned the GaN sample with (HCL:HNO3 3:1) for 15 min then
used Acetone and methanol and finally DI water and blow dry with N before
doing lithography. I believe this is enough to clean the sample.

Any suggestions on how to deal with this problem???

your truly,

Ali